Basically Hashtag is Used For Search Such Important info that were update on IRI .
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Suppose if you update any info with hashtag like #WAP4 so in future if you want to search then go to Modify option >> write hashtag name >>Member/Admin Name .so you are easily get your blog Using hashtag .
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Basically...
more... it is used for future search . but better use this hashtag for useful information .
Happy to Help !!
Thanks